Buy an Audio Research SP10 MkII or an SP11 MkII ?

Growlar,
I've owned both the SP10 & SP11 with a D115. Overall, my preferance is the SP10 even though I ended up getting rid of it. As others have said, the line section of the SP10 is not up to par with the phono section. This is not really the line section per say but rather that to use the line stage, you have to switch off the by-pass which engages all of the front panel clap trap. The reason I got rid of mine in the end was I got tired of feeding it tubes. If I ever win the lottery, I will buy another of these and have it rebuilt by Great Northern Sound. It is a classic.

I owned an SP-10 and SP-11 too.I was not experienced enough at the time to really determine superiority of either unit.I did ultimately get an SP-15(I can hear the "HOOTS" from the tube crowd already).What I can say,with confidence,is that after sending this unit to Great Northern Sound,for a complete rebuild(their ref update),I have to laugh at some of the prices asked for todays top contenders.I now have a supremely quiet,and neutral linestage,coupled to an unbelieveably high quality phono section.Tube rolling(3 tubes in phono section)does not cost an arm and a leg,and does make a big difference.I now have a very high quality Avalon based system,and find the pre/phono to have NO signature,tube or solid state.That is the way I want it.I have a friend who had the exact upgrade done and is also ecstatic with the results.He is an experienced tube lover(as I have become),but both of us realise that a truly neutral sound that can be nudged one way or another(for vinyl)by only three tubes is a pleasure to listen to.Good luck.

I'm confused ... what does Tube Rolling mean ? I've got that Homer Simpson far away look on my face.

put the tubes on the floor and roll... which tube goes further wins : )

What sirspeedy means is swapping different brand and model of tubes (like tires on your car) and you'll get different performance. Some do better in (wet, ice, dry pavement, sand..) clarity, body, extension, and presence.
It takes a lot of lab test ( trial and error ) to get the best performace you want for your taste of music.
It took me over 50 different 6DJ8/6922/7308 (except CCa because they're too expensive) tube families to get the way I like on the SP-11 MK II. I'm not big fan of SP-10 because it sounded a little slow and thick for my taste.

I'm the guy Jeffrey Behr referred to above and while it's been almost 20 years since I last heard an SP-10 (and 14 years since I heard the SP-11 Mk II I stashed in boxes back in 1991), having read this thread, I'll offer one more suggestion: If your amp is sensitive enough and your phono cartridge has enough output and you don't load it down too far, you just may be able to get away with using only the phono stage of the SP-11.

I was able to do this with HP's reference system back when I worked at TAS as well as my own system (just remember to invert phase at the speakers to make it an equal comparison) and if my memory serves me correctly, the stripped-down, "hot rod" version of the SP-11 was clearly preferred to the SP-10 that sat alongside it by pretty much everyone who heard the comparison.

YMMV, of course, but if you find a good deal on an SP-11 -- and come to think of it, mine might well be for sale -- it's an alternative you may wish to consider.